Did you check latest drivers on AMDs website? If the AMD software shows you have the lates version that might not always be 100% accurate (perhaps you have "look for optional drivers" disabled, etc.), check the website if maybe there has been a new driver version.
Other than that check what DirectX version you are running, I know Fortnite has dx11 and dx12 modes, perhaps the dx12 version requires a driver that your GPU might not have support for.
